1. Field of the Invention
The present invention generally relates to communication units, and more particularly to a communication unit which transmits packets in the form of Asynchronous Transfer Mode (ATM) cells.
Recently, communication systems which transmit data at a high speed in the form of packets, are widely used. On the other hand, networks are being realized which treat ATM cells conforming to the ATM which transmits information such as data at the high speed. In data transmission using the ATM cells, multiplexing is carried out for each Virtual Channel (VC), and for this reason, it is possible to efficiently utilize the transmission channel.
However, in a node or server which carries out a transmission control, it takes time to process, by a software process, the ATM cells which are multiplexed and form packets for controlling the protocol or the like. As a result, unused slots are introduced on the line, and there are demands to improve the operation efficiency of the line.
2. Description of the Related Art
FIG. 1 is a diagram for explaining an example of a conventional communication unit. More particularly, FIG. 1 shows the construction of a node or server within an ATM network. The node or server includes a Cell Assembly and Disassembly (CLAD) and Direct Memory Access Control (DMAC) part 80, a buffer memory 81, a Central Processing Unit (CPU) 82, and a gate 83.
In the conventional ATM network, a packet of user information from a terminal (not shown) accommodated in each node is transmitted in the form of ATM cells respectively made up of a 5-byte header and a 48-byte information part. A large number of such packets of the user information, that is, user packets, are transmitted in the form of multiplexed ATM cells, and each user packet is distinguished by a Virtual Channel (VC) which is set in the header. In addition, protocol packets are transmitted on the line in the form of the multiplexed ATM cells together with the user packets. The protocol packets are packet information for controlling the protocol, and are used to control transmissions in the network.
The ATM cells of the user packets and the protocol packets are input to the CLAD and DMAC part 80 from an input line. In this particular example, the user packet is transmitted in the form of 2 kinds of ATM cells {circle around (1)} and {circle around (2)} respectively having VCs 100 and 101, and the protocol packet is transmitted in the form of ATM cells {circle around (3)} having a VC 10. A plurality of such ATM cells {circle around (1)}, ATM cells {circle around (2)} and ATM cells {circle around (3)} are multiplexed and transmitted. When the plurality of kinds of ATM cells {circle around (1)}, {circle around (2)} and {circle around (3)} are multiplexed and input to the CLAD and DMAC part 80 via the input line, the following processes A, B and C are carried out in this sequence.
Process A: The CLAD and DMAC part 80 identifies the VC in the header of each ATM cell, and sequentially stores, by a DMA transfer, the 48-byte information parts which are deleted of the headers of the ATM cells in corresponding regions of the buffer memory 81 for each of the VCs, so that the original packets can be assembled.
Process B: The assembled packets in the buffer memory 81 are processed by a software processing of the CPU 82, in a sequence starting from the packet the assembly of which is completed. The software processing in this case mainly processes the transfer control with respect to the protocol packet.
Process C: After the software processing ends, a DMA transfer is carried out and a cell header is thereafter added to output the ATM cells to an output line. In this particular case, 3 ATM cells forming the protocol packet {circle around (2)} having the VC 10 are sequentially transmitted, and after a predetermined time corresponding to the software processing, 2 ATM cells forming the user packet {circle around (1)} having the VC 100 are sequentially transmitted, followed by 2 ATM cells forming the user packet {circle around (3)} having the VC 101.
As described above, the packets are processed by the software processing, and the output is thereafter made for each of the packets. As a result, a large amount of empty cell spaces, that is, gaps, are formed between the packets which are output, and there is a problem in that the line cannot be utilized efficiently. In addition, because of the limit in the processing speed of the software processing, there are problems in that the increase in the line speed and capacity is limited thereby.
Accordingly, it is a general object of the present invention to provide a novel and useful communication unit in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a communication unit which transmits packets in the form of ATM cells by multiplexing VCs, so as to be unaffected by effects of a software processing of protocol packets, and to realize a high-speed transmission and a large capacity of a line without introducing gaps on the line.
Still another object of the present invention is to provide an apparatus comprising a packet buffer receiving Virtual Channel (VC)-multiplexed ATM packets from an input line, judging a packet type, converting a header and assembling a packet, a protocol processor receiving and processing a protocol packet output from the packet buffer when the packet type of the packet assembled in the packet buffer is the protocol packet, and a packet output scheduler which carries out an arbitration in response to a reception of a user packet from the packet buffer and an ending of a process from the protocol processor, and selects and outputs to an output line the user packet or the protocol packet based on the arbitration. According to the apparatus of the present invention, it is possible to carry out the processes of forming the packet from the cells, converting the header and processing the protocol at a high speed, and also sufficiently utilize the line rate. For this reason, the present invention is particularly effective when applied to a unit which is used in an internet network in which large amounts of header conversion and protocol processings are made and the data are exchanged in units of packets. Thus, the present invention can cope with the continuously increasing internet demands, and increase the speed of the line as well as enable efficient use of the line.
A further object of the present invention is to provide a communication unit which transmits packets in the form of ATM cells, comprising a packet buffer part receiving Virtual Channel (VC)-multiplexed ATM cells from an input line, judging a packet type, converting a header and assembling a packet, a protocol processing part receiving and processing a protocol packet output from the packet buffer part when the packet type of the packet assembled in the packet buffer part is the protocol packet which is used for communication control, and a packet output scheduling part, including a scheduler which carries out an arbitration when an output request generated upon completion of a reception of a user packet from the packet buffer part and an output request generated upon ending of a process from the protocol processing part are received, and selects and outputs to an output line the user packet or the protocol packet based on the arbitration. According to the communication unit of the present invention, it is possible to carry out the processes of forming the packet from the cells, converting the header and processing the protocol at a high speed, and also sufficiently utilize the line rate. For this reason, the present invention is particularly effective when applied to a unit which is used in an internet network in which large amounts of header conversion and protocol processings are made and the data are exchanged in units of packets. Thus, the present invention can cope with the continuously increasing internet demands, and increase the speed of the line as well as enable efficient use of the line.
Another object of the present invention is to provide a communication unit which transmits packets in the form of ATM cells, comprising a packet buffer part receiving Virtual Channel (VC)-multiplexed ATM cells from an input line, a packet output scheduling part having a scheduler, and a protocol processing part, where the packet buffer part includes a packet type judging part judging a packet type of the received ATM cells, first and second packet assembling parts assembling a packet from the received ATM cells, first and second packet buffer parts, and first and second packet output parts, the first packet assembling part, the first packet buffer part and the first packet output part are provided with respect to a protocol packet, the second packet assembling part, the second packet buffer part and the second packet output part are provided with respect to a user packet, the first packet output part outputs the protocol packet with respect to the protocol processing part, the second packet output part has an output arbitration part which carries out an arbitration between the scheduler of the packet output scheduling part and outputting the user packet to the packet output scheduling part, and the protocol processing part outputs the protocol packet to the packet output scheduling part when a software processing of the protocol packet ends. According to the communication unit of the present invention, it is possible to carry out the processes of forming the packet from the cells, converting the header and processing the protocol at a high speed, and also sufficiently utilize the line rate. For this reason, the present invention is particularly effective when applied to a unit which is used in an internet network in which large amounts of header conversion and protocol processings are made and the data are exchanged in units of packets. Thus, the present invention can cope with the continuously increasing internet demands, and increase the speed of the line as well as enable efficient use of the line.